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An 8-year-old boy was in the hospital Wednesday night after undergoing surgery to remove shrapnel from his eye. Metal pieces flew into the boy’s eye when another child pulled the trigger on an AR-15 rifle that was mounted on a police officer’s motorcycle during a safety presentation at a Chino elementary school that morning. Gadi Schwartz reports for the NBC4 News at 11 p.m. on Oct. 23, 2013. (Published Thursday, Oct 24, 2013)

Updated at 4:47 AM PDT on Thursday, Oct 24, 2013

Three students were hurt when a child fired an officer's rifle during a safety presentation at a Southern California elementary school Wednesday, authorities said.

It happened about 11:15 a.m. at Newman Elementary School in Chino (map), according to Tamrin Olden, crime prevention supervisor for the Chino Police Department.

Investigation After Gun Discharges at Elementary School

Three children were harmed when a gun went off during a safety training class at a Chino elementary school. Investigators are trying to figure out why it was left unattended. Tony Shin reports from Chino for the NBC4 News at 5 p.m. on Oct. 23, 2013. (Published Wednesday, Oct 23, 2013)

The child fired a loaded AR-15 rifle, which was mounted on a police motorbike on on display in the school's courtyard, a school official said.

Two students were taken to the hospital with minor injuries, Olden said. A third student was treated at the school and sent home.

An uncle for one of the injured students told NBC4 Los Angeles that his 8-year-old nephew was hit by metal fragments after an officer's bullet struck the ground. The boy was recovering Wednesday evening after he underwent surgery to have shrapnel removed from his eye.

He said another child who was playing near his nephew was also struck by metal fragments. No one suffered a gunshot wound, authorities said.

Officers were on the Chino campus for a Red Ribbon Week event, a national initiative aimed at preventing drug use among children and teens.

After the incident, school officials sent an emergency voicemail to parents containing limited information.

"It was an accidental discharge and that two children were injured," parent Tim Everman said, describing the contents of that automatic message.

Parents are demanding answers as to why officers left a loaded weapon on display around young children. Investigators are probing why the firearm -- the type of which has not been identified -- was left unattended.